It has been known that coils for controllably deflecting a charged-particle beam in an electron microscope or the like are fabricated by printing plural scroll coil circuits on a flexible insulating sheet. Techniques of this kind are disclosed, for example, in Japanese Patent Unexamined Publication Nos. 160947/1984 and 60563/1977.
Techniques for fabricating deflection coils by printing scroll coils with a conductive material on both sides of an insulating sheet and winding the sheet into a cylinder are disclosed in these Patent Publications.
The above-described prior-art techniques fail to take account of a case in which the number of printed scroll coils stacked on top of each other is increased to produce a strong deflecting magnetic field. Accordingly, with these prior-art techniques, it is difficult to construct small-sized coils capable of accurately developing a strong deflecting magnetic field in a desired direction, for the following reasons.
In order to fabricate coils for producing a strong magnetic field in a desired direction with high accuracy, using the aforementioned printed circuit, the following requirements (a) and (b) must be satisfied.
(a) In order to setup a strong magnetic field, it is necessary to stack a number of scroll coils printed on the printed circuit on top of each other. One conceivable method of arranging these printed scroll coils so as to stack them on top of each other is to wind the printed circuit into a cylinder in plural layers. Another conceivable method is to fold the printed scroll coils. Where the former lap-winding method is adopted, it is necessary to place the stacked scroll coils in position circumferentially accurately.
(b) In order to develop a strong magnetic field, it is necessary that the scroll coils be excited with greater currents.
However, where the above-described lap-winding method is utilized, if the printed circuit is wound in more layers in order that more scroll coils be stacked, then outer scroll coils are shifted circumferentially with respect to inner scroll coils. This causes a deviation of the direction of the produced magnetic field from the intended direction.
Where the number of printed scroll coils is increased, if these numerous scroll coils are connected in series, the resistance is increased, thus resulting in decreases in currents flowing through the scroll coils. Therefore, connecting too many scroll coils in series is undesirable. Accordingly, if a multiplicity of scroll coils are connected in parallel, each scroll coil needs a feeding external connector terminal and a connector lead that connects this coil to the external connector terminal. If the number of external connector terminals is increased, it is cumbersome to make a connection with an external circuit.